Four basic aspects of mineralization in bones and teeth are being investigated by light microscopy, autoradiography and electron microscopy: cell differentiation, development of hard tissue matrix, calcification of the matrix, and resorption of bone mineral. Sharks, bony fishes and frogs will be used for experiments and for histological studies. An experiment with a radioactive precursor, the amino acid proline, will be conducted to determine source of the protein fibrils in the enamel of sharks' teeth. Fibillogenesis of the connective tissue protein collagen will be studied in tissue from shark fins and from the adipose fins of certain teleost fishes, including synodontids and salmonids. Large collagenous fibers known as ceratotrichia or actinotrichia develop in these fins and are useful as models of fiber growth. An agent known to affect collagen crosslinking, beta-aminopropionitrile, has been tested for its influence on fibrillogenesis and mineralization in fish fins and frog limbs. Histological analysis will continue. Other agents known to affect mineralization will be tested for their effects on limb bone development in tadpoles of Rana pipiens. They include gamma radiation, thyroxine, parathormone, thyrocalcitonin, prolactin, cortisone, actinomysin D, chloramphenicol, and malathion.